Production of nu-substituted furfurylamines



Patented Aug. 24, 1948 PRODUCTION or n-sons'rrruruo ruaruan.

AMINES Ever-ct F. Smith, Terre Haute, Ind; assignor to CommercialSolvents Corporation, Teri-e. Haute, Ind., acorporation of Maryland NoDrawing. Application February 9, 1946,

Serial No.846,!m3

' .fi'Glaims. (01. 1266-345! 1 .Thisinvention relates toa process torpreparing secondary amines io'y catalytically reacting :a primary amine;a ketone, and hydrogen. More particularly, the invention relates to aprocess for preparing N-substituted furiurylamines by reactingmonofurfurylamine with an aliphatic ketone and hydrogen in the presenceof a metal chromite catalyst. In one specific embodiment the inventioncomprises reacting tetrahydrofurfurylamine with acetone andhydrogen inthe presence of copper chromite catalyst to produceN-isopropyltetrahydrofurfurylamine.

The formation of secondary :amines from primary amines, ketones, andhydrogen is a chain reactionthattakes place inthnee steps: =(1)Condensation-ot therhe'tone with-the-amine to form-an unstableintermediate, 2-) dehydration of the intermediate compound to -form-alease, and i3 hydrogenation of the S'chtfi loase 'to the desired famine.Inacatrying out this series-oi reac- I tio'ns, however, one-or morecompeting reactions are commonly encountered. Certain catalysts, such asHaney nickel, for example, tendto favor the direct hydrogenation of the'ketone to the corresponding alcohol, and thus to give :low yields,based on the ketone; Certain other catalysts,suchas-palladium,'tencltoiavor another chain reaction, in which theketone condenses-with itself to form-a keto alcohol, the*ketoalcoholdehydr ates :to an unsaturated lie-tone; and the unsaturatedke'to-ne is partially hydrogenated to a saturated ltetonehaving twice asmany carbon atoms as the original ire-tone. My invention rests in thediscovery that metal "chromite catalysts, particularly copper chromite,selectively catalyze the conversion of monofurfurylamines, ketones, andhydrogen-to secondary amines.

The amine used in my process may he any primary amine of the type'R'NH-zin which R is the furfuryl group or a derivative thereof. As examples ofsuch amines may be cited *furiuryl'amlne and tetrahy-drofur'furylarnine.

'The ketone used in my process may he all-cyclic, suchas' cyclohexanone;or it maybe aralkyl, such 'as acetophenone; but it is preferably analkyl 'ketone, such as acetone, ethyl methyl ketone, diethyl ketone,isobutyl methyl ketone, or amyl methyl ketone.

By a suitable choice of primary amine and ket'one, it' is' possible toproduce secondary amines having a wide range of structure, a'wide rangeof physical properties.

Hydrogen of a relatively high degree of purity is preferred for use inmyprocess. It need not be absolutely pure, hut reactive lmpuritiessuch-as oxygen should be kept as low :as possible, and catalyst poisons;such as hydrogen sulfide, should be excluded altogether. Inertimpurities such as nitrogen are undesirable because they increase thetotal pressure in the reaction vessel necessary to 2 mamtain therequired partial pressure or hydrogen. :For this reason, the proportionof inert .hnpurities should be kept as :low as possible.

A metal chromite catalyst suitable for use in my process may be producedaccording to: the method of Calingaert and Edgar (1nd. Eng. Chem" 26,-8-8130 i1=934)).. This methodcomprises generally reactingsa coppersalt, such as sulfate, with the- *dichromate of an zaikali metal such.as .sodiuIn,,-andi ammonia, to form a precise!- tate :of copperammonium chromate; avhichzis then washed, dried, and roasted to produce[copper chromite suitable for use in. my :process known methods may beused for producing chromite catalysts satisfactory tor use in myprocess, the procedure of Calingaert :andiildgar being cited merely as aconven-ient and desirable method.

The inclusion of various "additives in thereaction mixture, asrecommended in the prior art, has given generallypoor results- "in myprocess. Calcium oxide, for example, which: is repor ted' act "as astabilizer for copper chromite, tends to increase the hydrogenation ofthe hetone tothe corresponding alcohol. Moreover, alkali-metal salts ofweak organic acids, such-as sodium =ta-te, which are reported to"increase the conversion in one process-for making secondary amines,have shown the opposite effect in my process.

In the reactionof primary amines with lcetones to form secondary aminesas the ultimate "proctu'ct, the stoichiometric molarratio is l 1, hutthe process is operative to some degree over a wide range of reactantratios, with either theprimary amine or "the ketone in excess. However,since any excess ketone is ordinarily hydrogenated to the correspondingalcohol, and since under any circumstances there'is a tendencytowardhydro- .g'enation of a substantial proportion of the ketone, theuse of an excess of the primary amine ispreferred in order tohold theloss of ketone to 'a'mlnimum. For best conversions andyiel'ds, an excessof approximately 5 to'20% of the primary amine has been f oundjprefera'bl'e.

The temperatures employed are preferably of the order of '100, to C.,butmay extend over a, range of about 751301225" 0. At temperatures above.225 C,., destructive reactions 'begin'to take place, and .thehydrogenation less selective. .A't temperatures approaching 1Z5 0., thereaction becomes comparatively slow, and substantially higher pressuresare required .to make the retrotion proceed at a practical rate.

Pressures up =to 5000 pounds .per square inch or more maybe employed,but are preferably with in the range of 250 to 2000 pounds per squareinch. .As indicated above, the higher temperatures permit the use oflower pressures, wl-ulemt the lower temperatures, the hydrogen pressuremust be increased in order to maintain a satisfactory hydogenation rate.For any particular combination of primary amine andketone; how ever, Ihave found that the maximum conversion and yield are obtained within acomparatively narrow and specific temperature range and with in acomparatively narrow and specific, pressure per square inch prior to theinitiation of the range. For example, in the production of Nisopropyltetrahydrofurfurylamine from tetrahydrofurfurylamine andacetone, the maximum con-- version and yield are obtained at about-150C5 and 1000 pounds per square inch.

1000 pounds per square inch.

hydrogenationp and as the hydrogenation proceeded, .iresh' hydrogen wasintroduced from time to time to restore the pressure to its initiallevel of A total pressure drop of 1400 pounds per square inch took placein In carrying out my process, a mixture .of the reactants and catalystmay be introduced into a pressure vessel equipped with a suitablestirrer and a jacket or coil for maintaining the charge at the propertemperature. Hydrogen is then injected to the desired pressure, and theautoclave is heated to the desired reaction temperature. During thereaction, hydrogen is added either intermittently or continuously asrequired to maintain the pressure at the desired level. When thehydrogenation has been completed, as evidenced by the cessation ofhydrogen absorption, the reaction mixture is cooled, the autoclave isvented, the contents are discharged, and the product is isolated in aknown manner.

Alternatively,-I may carry out my process by passing a slurry of thepowdered catalyst in the liquid reaction mixture through a column incontact with hydrogen gas under proper conditions of temperature andpressure. Or I may pass the reaction mixture through a stationary bed ofpelleted or supported chromite catalyst, enclosed in a reaction vesselof suitable design.

Foruse in the production of secondary amines,

copper chromite possesses numerous advantages over other hydrogenationcatalysts: I

1. Copper chromite is cheaper than nickel, platinum and palladiumcatalysts.

2. Copper chromite is easily and conveniently prepared in asemicontinuous unit.

3. Copper chromite is non-pyrophoric, and hence is safer than manycatalysts to make and to handle.

4. Unlike nickel, platinum, and palladium, copper chromite is resistantto poisoning.

-5. Unlike poison-resistant sulfide-type catalysts, copper chromite isactive at comparatively low temperatures and pressures.

6. Copper chromite not only has a long life, but maintains its initialactivity longer than do other catalysts.

7. In the presence of copper chromite, the hydrogenation of Schiff basesproceeds at a substantially faster rate than the hydrogenation ofketones. Nickel catalysts tend to produce the opposite efie ct.

, 8. According to the prior art, nickel produces tertiary amines fromprimary amines, ketones, andhydrogen. Copper chromite does not, I

9. Palladium catalysts produce a substantial conversion of ketones tohigher-boiling ketones in the presence of alkaline materialssuch as prlmary amines. Copper chromite does not.

The following example is given to illustrate my invention, and is not tobe construed as limiting it to the exact reactants or conditionsdescribed:

A mixture of 184 g. acetone, 352 g. tetrahydrofurfurylamine, and 10.7 g.copper chromite was introduced into a stainless-steel rocking bombhaving a total volume of 1840 ml., and the bomb was sealed andtransferred to a rocking unit oscillating at the rate of 37 cycles perminute. Hydrogen was injected to a pressure of 1000 1.0'hou'r,' at theend of which time the hydrogenation wascomplete. The bomb was thencooled and emptied, and the product was filtered to remove the catalystand subsequently fractionally distilled through a laboratory columnpacked with single-turn glass helices. The following materials wereseparated? 53 g. tetrahydroiurfurylamine and 326 g.N-isopropyl-tetrahydrofurfurylamine, boiling point (uncorr.) 56-57 C. at10 mm.

Conversion: Per cent On ketone '72 On amine 65 Yield:

On ketone 72 On amine--. 77

I claim as my invention:

1. A process for producing secondary amines which comprises reacting amonofurfurylamine' with a ketone and hydrogen in the presence of a metalchromite hydrogenation catalyst.

2. A process for producing secondary amines which comprises reacting aprimary amine chosen from the group consisting of furfurylamine andtetrahydrofurfurylamine with a ketone and hydrogen in the presence of ametal chromite hydrogenation catalyst.

3. A process for producing secondary amines which comprises reacting aprimary amine chosen from the group consisting of furfurylamine andtetrahydrofuriurylamine with an alkyl ketone and hydrogen in thepresence of a copper chromite catalyst.

4. A process for producing N-isopropyltetrahydrofurfurylamine whichcomprises reacting tetrahydrofurfurylamine with acetone and hydrogen inthe presence of a copper chromite catalyst.

5. A process for producing secondary amines which comprises reacting aprimary amine chosen from the group consisting of furfurylamine andtetrahydrofurfurylamine with an alkyl ketone and hydrogen at atemperature between about 7 5 and 225 C. and at a pressure between about250 and 5000 pounds per square inch in the presence of a copper chromitecatalyst.

6. A process for producing N-isopropyltetrahydrofurfurylamine whichcomprises reacting tetrahydrofurfurylamine, acetone, and hydrogen at atemperature of about -150 C., and a pressure of about 250-2000 poundsper square inch in the presence of a copper chromite catalyst.

. EVERET F. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent: 1

UNITED STATES PATENTS Date Winans Oct. 8, 1940 Certificate of CorrectionPatent No. 2,447,823. August 24, 1948;

EVERET F. SMITH It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows: Column 4, line 59, claim 6, for BO-150 0. read 100150 0.; andthat the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 30th day of November, A. D. 1948.

[SEAL] THOMAS E. MURPHY,

Assistant Commissioner of Patents.

